what does vu3d use?
On 05/08/2009, Thomas Harte <[email protected]> wrote: > > That's not entirely true. Matrices are numerically unstable, so the > cost of ensuring they remain orthonormal when applying consecutive > local transforms in a game such as Elite is substantially greater than > the cost of ensuring that a quaternion remains of unit length. > > I make it 8 multiplies, 3 adds, 1 square root and 1 divide to fix up > numerical error in a quaternion. Conversely, I get 36 multiplies, 21 > adds, 3 square roots and 3 divides to fix up an orthonormal matrix. > > Quaternion to matrix is 10 multiplies, 6 shifts and 14 adds. So the > way I calculate it, you can fix a quaternion and convert it into a > matrix in less than you can fix up a matrix. Furthermore, quaternion > composition is 16 multiplies and 12 adds, whereas matrix composition > (with assumptions about the bottom row of a 4x4) is, ummm, at least 36 > multiplies and 18 adds. And that's with the translation component not > completely factored in (I'm reading actual code off screen and have > optimised the translation out of this particular batch). > > Elite is also a perfect example of when Euler's aren't fine, even if > they didn't produce Gimbal lock, as all rotation is around local axes. > And besides that, Euler angles always have to be converted to some > other form before they can be applied to arbitrary geometry. Matrices > require no further transforms. > > On Wed, Aug 5, 2009 at 2:12 AM, Simon Cooke<[email protected]> wrote: > > You only really need quaternions if you're doing animation or > interpolation. > > If you can live with the gimble lock, euler's fine. > > > > -----Original Message----- > > From: [email protected] [mailto:[email protected]] > On > > Behalf Of Thomas Harte > > Sent: Tuesday, August 04, 2009 10:05 AM > > To: [email protected] > > Subject: Re: Hi - just checking > > > > Am I replying to the correct thread? I don't know. But I've had the > > opposite experience to a bunch of people here, having become > > substantially more busy in my work than I was even just a few months > > ago, squeezing the SAM temporarily out. > > > > A version of my vector 3d-stuff-as-a-library-for-others was all but > > finished several months ago, I'll endeavour to get that out, though it > > still has the awkward limitation of doing rotations with Euler angles > > only - which may be less efficient and is certainly more limiting than > > special orthogonals or quaternions. > > > > I'm still thinking about smart ways to optimise the reverse face > > stuff. I need to get something hierarchical or otherwise group-related > > in there; checking every single face is obviously not the optimal way > > to proceed. I guess what I'm looking for is some sort of bin-type > > mapping to the surface of the unit sphere that allows all the points > > on a particular hemisphere to be isolated from the majority of the > > points on the opposite hemisphere. Or, you know, something at least a > > lot like a sphere. Though I'm not sure any sort of lookup into > > something a lot like a sphere would help much as it'd need to be > > indexed by a three-tuple. > > > > I guess a good broad sweep would be to mark each face according to the > > visibility of the faces of a bounding box - if a face on the real > > model points away from the face on the bounding box then it definitely > > can't be visible if the box face is. Or something like that. > > > > I'm going to stop thinking aloud now... > > > > On Tue, Aug 4, 2009 at 10:22 AM, Steve Parry-Thomas<[email protected]> > > wrote: > >> I guess when the clocks go back in October SAM users will hibernate over > > the > >> winter until next August! > >> > >> > >> > >> > >> > >> > >> > >> From: [email protected] [mailto:[email protected]] > On > >> Behalf Of Ian Spencer > >> Sent: 04 August 2009 08:04 > >> > >> To: [email protected] > >> Subject: Re: Hi - just checking > >> > >> > >> > >> Wow, I just sent the checking mail to see whether something was wrong > with > >> my subscription to the group and it seems it was like poking a stick > into > > a > >> hornets nest (in a positive sort of way) - over 40 mails in the last few > >> days on the group. It's just great to see everyone is alive and kicking > > out > >> there. > >> > >> > >> > >> Ian > >> > >> > >> > >> ----- Original Message ----- > >> > >> From: Ian Spencer > >> > >> To: [email protected] > >> > >> Sent: Friday, July 31, 2009 4:10 PM > >> > >> Subject: Hi - just checking > >> > >> > >> > >> Not heard anything on the group for quite a while so just thought I > would > >> send a 'test' to check it's not me that's got a problem and say hi to > >> everyone. > >> > >> I know you've all taken your Sam's to the beach and so no activity on > the > >> group. > >> > >> > >> > >> > >> > >> Ian > >> > >> > >> > >> > > > > >
